The rotatable supporting structures of various types of mechanical devices are assembled with a rolling bearing such as a ball bearing, a cylindrical roller bearing, a tapered roller bearing or the like. This kind of a rolling bearing is provided with a seal assembly for the purpose of preventing the grease applied inside of this rolling bearing from leaking out of the rolling bearing, and also preventing various types of foreign objects such as rain water, mud, dust and the like from entering the inside of the rolling bearing. FIGS. 25 to 27 show three exemplary structures of the seal assembly provided at the opening of the end portion of a rolling bearing for this purpose.
First, the prior art structure as a first example illustrated in FIG. 25 is described in JP Patent Publication No. Tokukai Hei 10-252762 is composed of a metal core 5, a slinger 6 and a sealing member 7. The metal core 5 among these elements is formed as a generally annular ring having an L-shaped cross section, and composed of a radially outer cylindrical portion 9 which can be internally fitted and fixed to the inner peripheral surface of the end portion of an outer race 8 and an inner circular ring portion 10 which is bent inwardly in the radial direction at the inner end edge of this radially outer cylindrical portion 9 in the axial direction (the end edge located near the center of the rolling bearing in the axial direction, i.e., the left end edge as illustrated in FIG. 25). Also, the above slinger 6 is formed as an annular ring having an L-shaped cross section, and composed of a radially inner cylindrical portion 12 which can be externally fitted and fixed to the outer peripheral surface of the end portion of an inner race 11 and an outer circular ring portion 13 which is bent outwardly in the radial direction at the axially outer end edge of this inner cylindrical portion 12 (the end edge located near the opening of the rolling bearing in the axial direction, i.e., the right end edge as illustrated in FIG. 25). Furthermore, the above sealing member 7 is made of a resilient member, for example, an elastomer such as a rubber, and provided with three seal lips 14 to 16, i.e., an outer, an intermediate and an inner seal lip, whose base end portion is fixedly connected to the above metal core 5. The outer seal lip 14, which is provided in the most outer location, has its tip edge to be in slidable contact with the inner surface of the outer circular ring portion 13 of the slinger 6. On the other hand, the intermediate seal lip 15 and the inner seal lip 16, which are the remaining two seal lips, have their tip edges to be in slidable contact with the outer peripheral surface of the radially inner cylindrical portion 12 of the above slinger 6.
Also, in the first example as illustrated in FIG. 25, the thickness of the outer seal lip 14, which is located in the outermost position among these three seal lips 14 to 16 of the above sealing member 7, is gradually decreasing from the base end portion to the tip edge. Furthermore, the thickness of the inner seal lip 16, which is located in the most inner position, is gradually decreasing from the base end portion to the tip edge in the same manner. This inner seal lip 16 is tilted in the direction such that it goes outwardly in the axial direction of the rolling bearing toward the tip edge thereof. Also, the intermediate seal lip 15 located in the intermediate position has a thin base end portion, a thin tip edge and a thick intermediate portion.
Furthermore, the prior art structure as a second example illustrated in FIG. 26 is approximately similar as that of the above first example illustrated in FIG. 25. Particularly, in the case of this example, an outer seal lip 14a, which is located in the most outer position among these three seal lips 14a, 15a and 16, has the nearly same thickness throughout the entire length from the base end portion to the tip edge thereof. On the other hand, the intermediate seal lip 15a located in the intermediate position is designed to have a base end portion thinner than the tip end portion thereof. In contrast to this, in the case of the prior art structure as a third example illustrated in FIG. 27, the thickness of the outer seal lip 14 is gradually decreasing from the base end portion to the tip edge thereof in the same manner as illustrated in FIG. 25 showing the first example. The other structure of the third example is similar as that of the second example as illustrated in FIG. 26.
In any prior art structure of the first to third examples as described above, the opening of the end portion of the rolling bearing is blocked with the slinger 6 slidably contacting the tip edge of the seal lip 14, 14a, 15, 15a or 16 of the sealing member 7. This result in preventing the grease applied inside of this rolling bearing from leaking out of the rolling bearing, and also preventing various types of foreign matters such as rain water, mud, dust and the like from entering the inside of the rolling bearing.
There is desired, in the case of the three exemplary prior art structures as illustrated in FIG. 25 to FIG. 27, the improvement of the following points. That is, for example, in the case where the three exemplary prior art structures are applied to a rolling bearing to be incorporated into the support device for the wheels of an automobile, there may occurs a relative tilt between the inner race 11 with the externally fitted slinger 6 and the outer race 8 with the internally fitted metal core 5 (misalignment between the central axes of the respective members 11 and 8) when the automobile takes a rapid turn. If the inner and outer races 11 and 8 are relatively tilted, the above slinger 6 and the metal core 5 move partially close to each other so that the above respective seal lips 14, 14a, 15, 15a and 16 are excessively compressed. Also, if the inner race 11 is decentered from the outer race 8 for some reason, the above respective seal lips 14, 14a, 15, 15a and 16 may be excessively compressed. When the respective seal lips 14, 14a, 15, 15a and 16 are excessively compressed, the so-called pressing force is increased which is a force urging the tip edge of the seal lips 14, 14a, 15, 15a and 16 against the slinger 6. Because of this, the tip edges of the respective seal lips 14, 14a, 15, 15a and 16 tend to wear, and therefore the sealing performance is degraded at the slidably contacting region between the slinger 6 and the respective seal lips 14, 14a, 15, 15a and 16. Also, in this case, the rotating torque applied to the rolling bearing increases. Furthermore, if the inner and outer races 11 and 8 are relatively tilted, the peripheral surfaces of both the inner and outer races 11 and 8 move partially apart from each other to decrease pressing force of the seal lips 14, 14a, 15, 15a and 16 and increase the degree of risk that rain water and the like enters the inside of the seal assembly. Taking into consideration this situation, it is thought to increase the initial interference of the above seal lips 14, 14a, 15, 15a and 16 to increase the above pressing force in whole. However, in this case, when the inner and outer races 11 and 8 are relatively tilted, the pressing force of the above seal lips 14, 14a, 15, 15a and 16 can be furthermore increased near the peripheral surfaces thereof close to each other. Because of this, the tip edges of the respective seal lips 14, 14a, 15, 15a and 16 would wear, and therefore the sealing performance would be furthermore degraded. Also, the rotating torque applied to the rolling bearing would increase.
In any prior art structure of the three examples as described above, the interference between the slinger 6 and the tip edges of the intermediate seal lips 15 and 15a and the outer seal lips 14 and 14a is not suitably controlled. On the other hand, if this interference is excessive, the tip edges of the above intermediate and outer seal lips 15, 15a, 14 and 14a tend to wear, and therefore the sealing performance is degraded in the long term use at the slidably contacting region between the slinger 6 and the respective the seal lips 15, 15a, 14 and 14a. Also, in this case, the rotating torque applied to the rolling bearing (rotational resistance) increases. Conversely, if the interference between the slinger 6 and the tip edges of the above intermediate and outer seal lips 15, 15a, 14 and 14a is excessively small, the pressing force of the respective seal lips 15, 15a, 14, 14a against the slinger 6 is excessively decreased. In this manner, also in the case where the pressing force is excessively decreased, the sealing performance is degraded at the respective slidably contacting regions. The inventors of the present invention therefore considered that the above interference needs to be controlled within an appropriate range for the purpose of improving the sealing performance of the respective slidably contacting regions.
Also, in the case of the second exemplary prior art structure as illustrated in FIG. 26, since the outer seal lip 14a has the nearly same thickness throughout the entire length from the base end portion to the tip edge, there are the following shortcomings to be improved. Namely, if the outer seal lip 14a has the nearly same thickness throughout the entire length in this manner, this outer seal lip 14a tends to excessively bend at the base end portion (the root portion) when this outer seal lip 14a is urged against the slinger 6. When the outer seal lip 14a excessively bends at the base end portion (the root portion), a large strain is generated near the base end portion. Because of this, the motion following performance of the outer seal lip 14a responsive to the surface movement of the slinger 6 is degraded by the increasing resistance against the elastic deformation of the sealing member 7 made of a resilient member such as a rubber or the like. Also, in this case, since the stress relaxation occurs in the vicinity of the above base end portion, the pressing force of the above outer seal lip 14a on the above slinger 6 is decreased with the elapse of time. Accordingly, after long term use, the sealing performance tends to be degraded at the slidably contacting region between this outer seal lip 14a and the above slinger 6.
In contrast to this, in the case where the thickness of the outer seal lip 14 is gradually decreasing from the base end portion to the tip edge as illustrated in FIG. 25 and FIG. 27 showing the first and third examples, the strain in the vicinity of the base end portion can be decreased. However, the strain at the tip end portion of the above outer seal lip 14 is large instead. For this reason, in the same manner as the above second example, the motion following performance of the outer seal lip 14 responsive to the surface movement of the slinger 6 is degraded, and the pressing force of this outer seal lip 14 is decreased in the long term use. Also, in this case, as illustrated in FIG. 27 showing the above third example, the tip end portion of the outer seal lip 14 tends to come into surface contact (surface-to-surface contact) with the inner side surface of the outer circular ring portion 13 constituting the slinger 6. Then, when the tip end portion of the outer seal lip 14 comes into surface contact in this manner, the surface pressure is greatly decreased at the contact portion between the tip end portion of this outer seal lip 14 and the inner side surface of the outer circular ring portion 13 such that the sealing performance is easily degraded.
Also, in practical use of the seal assembly for the rolling bearing, the slinger 6 rotates with displacement in the axial and radial directions relative to the sealing member 7 in accordance with the misalignment of the respective components, the elastic deformation thereof and so forth. Because of this, even in the case where the outer seal lip 14a has the nearly same thickness throughout the entire length as illustrated in FIG. 26 showing the above second example, the above outer seal lip 14a can come into surface contact with the inner surface of the outer circular ring portion 13 when the slinger 6 moves toward the sealing member 7. Incidentally, if the entire length of the above outer seal lips 14 and 14a is made small, it is possible to suppress the above surface-to-surface contact. However, in this case, it becomes difficult to secure the sealing performance when the above slinger 6 moves apart from the above sealing member 7. Taking into consideration the above situation, the above outer seal lips 14 and 14a cannot be shortened so much.
On the other hand, in the three exemplary prior art structures as described above, when a hard foreign matter is bitten at the slidably contacting region between the tip edge of the outer seal lips 14 and 14a and the inner side surface of the outer circular ring portion 13, the abrasion at this slidably contacting region excessively progresses. The sealing performance at the above slidably contacting region is therefore largely lowered in a short period of time after the excessive progress of abrasion. In contrast to this, it is thought to prevent the above foreign matter from being bitten by increasing the pressing force of the outer seal lips 14 and 14a onto the slinger 6. However, in this case, the abrasion of the tip edge of the outer seal lips 14 and 14a is even more likely to make it difficult to secure a sufficient sealing performance. Also, it is thought to provide another seal lip, as a part of the sealing member 7, projecting from a position apart from the base end portion of the outer seal lips 14 and 14a for the purpose of preventing foreign matter from being bitten at the slidably contacting region between the tip edge of the outer seal lips 14 and 14a and the inner surface of the outer circular ring portion 13 by means of this another seal lip. However, the provision of such another seal lip may increase the torque of the rolling bearing and substantially raise the cost of the seal assembly for the rolling bearing.
Taking into consideration the above circumstances, the present invention is made for the purpose of improving the sealing performance of a seal assembly.